The present invention generally relates to a shrink wrap packaging apparatus and in particular to an apparatus for cutting shrink wrap film prior to the shrink wrapping operation.
In single roll shrink wrapping, a single sheet of shrink wrap film is wrapped around the product and into a tubular form. The overlapping lateral edges are located beneath the product and are sealed or otherwise joined together. During shrinking in a heat tunnel, the longitudinal edges of the shrink wrap film collapse against the ends of the product creating bullseye-type openings.
Various deficiencies exist in prior shrink wrap packaging and the methods of its fabrication. The single sheet of shrink wrap film was typically cut from a supply roll of the film. A common manner to cut the sheet from the web of film was to engage the film with a hot iron to melt the film and thus sever the sheet from the film. This hot iron is a high wear component and is always a source of operational problems. Another approach is to utilize a rotary blade which cuts the film. However, this approach experienced problems that the new leading edge of the web of film did not continue to follow the desired path of the film as a result of the velocity of the film and air resistance, the memory of the film, and/or the snap back of the film when the tension was released on the film because of cutting. These problems were overcome by cutting the film while the film is held across the cut and/or by including mechanical devices which grasp and pull the new leading edge, but such approaches unduly complicated the construction of the apparatus. Thus, there continues to be a need for feeding the film after a sheet is cut from the free end thereof which overcomes the deficiencies of the current approaches.
U.S. Pat. No. 5,771,662 (Struges et. al.), herein incorporated by reference, discloses an apparatus and methods for producing shrink wrap packaging. However, the Struges patent does not fully overcome the deficiencies of prior approaches, particularly in the area of cutting the film. Struges requires a vacuum table at the exit from the nip rollers to hold the film for further processing. The vacuum table is an expensive and complex piece of equipment which is not necessary for lower-speed operation. In addition, Struges requires a cutting blade that cuts tie strips into the film that allow the trailing edge of a single sheet of film which is downstream from the cut to remain connected to a new leading edge for the web of film which is upstream from the cut, so that the single sheet of film remains attached to the web of film thereby pulling the leading edge of the web of film toward and through the downstream pinch rollers 14 and 15 and to maintain tension of film between the upstream pinch rollers 12 and 13 and the downstream pinch rollers 14 and 15 and to ensure that the new leading edge of the web of film follows the desired path to the downstream pinch rollers.
The present invention overcomes the above deficiencies. It defines novel and non-obvious enhancements over the device described in U.S. patent application Ser. No. 10/960,238. In particular, it needs only a single nip roller pair rather than two roller pairs, it eliminates the need to keep tension on the film with the accompanying required programming complexity, it lessens snap-back of the film, and it eliminates folding-over the film by the second roller pair. Furthermore, the apparatus feeds the film so precisely even after it is cut, that the invention eliminates the need for an air knife to direct the new cut edge of the film into the rollers.